It's not the tempco of class 2 and 3 ceramics that are the problem. The capacitance varies with voltage which is a direct cause of 3rd order IM distortion. NPOs are needed anywhere you need to keep the signal clean. For a rail bypass cap, you might get away with a class 2 or 3. For a Miller cap, phase lead comp, coupling, or a tone control - don't.

It's not the tempco of class 2 and 3 ceramics that are the problem. The capacitance varies with voltage which is a direct cause of 3rd order IM distortion. NPOs are needed anywhere you need to keep the signal clean. For a rail bypass cap, you might get away with a class 2 or 3. For a Miller cap, phase lead comp, coupling, or a tone control - don't.

Oh, a big thing to make an audio oscillator using them as giant varicaps!